Study On The Effect Of Rare Earth Elements Yb On The Properties Of ZK60 Magnesium And A360 Aluminum Alloys

The effects of rare earth element Yb additions on microstructure and mechanical property of ZK60 Magnesium alloy and A360 Aluminum alloy have been investigated. The effect of Yb on ZK60, ZK60-1.0Yb and A360, A360-0.2Yb, A360-0.5Yb, A360-0.7Yb alloys under the condition of cast, extrusion, solution treatment, anneal and aging have been studied by use of OM, SEM, EDS, X-ray (XRD), DSC and micrhardness etc. The main research results are demonstrated as follow:(1)The evolution of microstructure of Mg-6Zn-lYb-0.6Zr wrought magnesium alloy which was prepared by gravity cast and hot extruded are investigated in this work. The cast ZK60-Yb alloy being machined to 45mm in diameter and homogenized at 340℃*8h+380℃*12h+440℃*24h, the ingots were then hot extruded to bars of 10mm in diameter at 370℃ with the extrusion ratio of about 20:1.The experimental results showed that Yb had an obvious effect on refining microstructures of ZK60-Yb alloys by restricting occurrence of dynamic recrystallization and preventing grain growth during extrusion and heat treatment. The Mg-Zn binary compounds in as-cast state were dissolved in matrix substantially and only a few particles remained during homogenization process. It is suggested that the dynamic precipitation was attributed to the dissolution of solute atoms supersaturated in matrix induced by dislocations. It could refine the DRX grains evidently and the plenty of fine dispersed spherical precipitates in grains could get effectively precipitation strengthening effect. It is proposed that the high performance wrought magnesium alloy with both grain boundary strengthening and precipitation strengthening could be prepared by the use of reasonable dynamic precipitation behavior and ideal dynamic phase precipitated.(2)The effects of Ytterbium on the microstructure and eutectic solidification behavior of Al-9.0%Si-0.25%Mg alloys were investigated.Microstructures of the alloys modified with different contents of Yb were analyzed by using of optical microscope (OM), X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) and mechanical properties were measured by hardness test. It was found that in metal casting method, addition of 0.7%wt Yb causes a structural transformation of eutectic silicon from a coarse plate to a fine fibrous morphology, in addition, Yb has the effects of grain refinement. It is concluded that the Yb atoms are incorporated into the silicon by adsorption at the solid-liquid growth front to cause modification of eutectic silicon.Furthermore, the results of XRD and EDS analysis reveal that the Yb-containing phase formed in the alloys is Al3Yb.